Effects of vagal cooling on esophageal cardiovascular reflex responses in the rat

Distension of the distal esophagus in the anesthetized rat causes a vagally-mediated arterial pressor and tachycardia response. To investigate the nature of viscerosensory fibers in the afferent limb of this reflex, the present study was carried out in urethane-anesthetized rats that were subjected to graded cooling of both cervical vagal trunks in situ. Distal esophageal distension was applied for 20 s by means of a water-filled high compliance balloon. Vagal cooling to 9 degrees C abolished pressor responses and unmasked a depressor component during maximal distension. Cooling to 7.5 degrees C blocked this inhibitory component, well above the temperature known to block C-fibers. We conclude that the cardiovascular response to esophageal distension is triggered via at least two subpopulations of A(delta) type vagal afferents that project to brain stem nuclei regulating central vasomotor tone.